Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $217.28   5.566%   $229.3738   $229.37   $229.35   $229.40  
  Purchase #2 $99.90   8.435%   $108.3266   $108.33   $108.35   $108.30  
  Purchase #3 $59.26   3.393%   $61.2707   $61.27   $61.25   $61.30  
  Purchase #4 $195.52   13.524%   $221.9621   $221.96   $221.95   $222.00  
  Purchase #5 $90.53   3.428%   $93.6334   $93.63   $93.65   $93.60  
  Purchase #6 $222.61   6.567%   $237.2288   $237.23   $237.25   $237.20  
  Purchase #7 $61.98   3.647%   $64.2404   $64.24   $64.25   $64.20  
  7 purchase totals = $947.08       $1,016.0358   $1,016.03   $1,016.05   $1,016.00